1. Field of the Invention
The present invention relates to a drive controller for a hybrid vehicle.
2. Description of the Related Art
From an environmental standpoint, it is desirable to have engine-driven vehicles emit as little environmental contaminants as possible. This interest has lead to the current development of hybrid vehicles mounted with an electric motor, in addition to an internal combustion engine, for driving the drive wheels of the vehicle.
A hybrid vehicle uses mainly an electric motor as the power source during steady running conditions to reduce noise and air pollution. A conventional hybrid vehicle also uses an engine in combination with the electric motor in order to compensate for the drawbacks inherent in an electric automobile driven by an electric motor. The additional use of the engine makes it possible to overcome the problems associated with driving the vehicle with the electric motor alone, such as the rather short distance that can be traveled on a single battery charge and the difficulty of effecting such operations as rapid start, high-load running, and high-speed running because the generated torque is small.
A hybrid vehicle can be a parallel type hybrid vehicle in which the drive wheels are alternatively driven by at least one of the engine and the motor according to the running conditions or the amount of electric energy remaining in a battery (secondary battery) that is charged by a generator. A hybrid vehicle can also be a series type hybrid automobile whose generator is driven by an engine, the generator generating electric power to operate a drive motor, which in turn drives the driving drive wheels.
Further, there also exist so-called series/parallel hybrid automobiles such as the one described in Japanese Patent Publication No. JP-U-Hei 2-7702, which combines the series type and parallel type hybrid structures.
With such a hybrid automobile (e.g., having both an engine and an electric motor as drive sources), when the output of the generator generated by the operation of the engine exceeds the power consumed by the motor, such as during low-speed, high-load running, the resultant surplus power is used to charge the battery.
However, an excessive charging current may be supplied to the battery, which may cause overheating of the battery. In this regard, the general construction of a hybrid automobile allows a sufficient space to be secured with respect to the mounting weight of the battery, which is calculated from the required drive force (discharging operation) corresponding to an operation by the user (vehicle driver). Thus, in a hybrid automobile, the permissible charging current for the battery is sufficiently large. That is, the hybrid automobile is mounted with a battery that is sufficiently large to permit supply of the charging current generated by the drive of the generator.
In recent years, it has been desired to mount the hybrid drive unit described above on two-wheeled vehicles, such as a motorcycle. In general, the space for mounting a drive unit in a two-wheeled vehicle is limited to the space between the front wheel and the rear wheel and under the seat within the vehicle body. Moreover, the width of a two-wheeled vehicle is also small as compared with that of an automobile.
For this reason, when mounting the hybrid drive unit constructed as described above to a two-wheeled vehicle, it is difficult to mount a battery of a volume sufficient to permit the supply of the charging current generated by the generator during low-speed, high-load running conditions or the like.